Methane fluxes in permafrost habitats of the Lena Delta: effects of microbial community structure and organic matter quality

For the understanding and assessment of recent and future carbon dynamics of arctic permafrost soils the processes of CH4 production and oxidation, the community structure and the quality of DOM were studied in two soils of a polygonal tundra. Activities of methanogens and methanotrophs differed significantly in their rates and distribution patterns among the two investigated profiles. Community structure analysis showed similarities between both soils for esterlinked PLFAs and differences in the fraction of unsaponifiable PLFAs and PLELs. Furthermore, a shift of the overall composition of the microbiota with depth at both sites was indicated by an increasing portion of iso- and anteiso-branched fatty acids related to the amount of straight chain fatty acids. Although permafrost soils represent a large carbon pool, it was shown, that the reduced quality of organic matter leads to a substrate limitation of the microbial metabolism. It can be concluded from our and previous findings firstly that microbial communities in the active layer of an Arctic polygon tundra are composed by members of all three domains of life, with a total biomass comparable to temperate soil ecosystems. And secondly that these microorganisms are well adapted to the extreme temperature gradient of their environment

Abundance, Distribution and Potential Activity of Methane Oxidising Bacteria in Permafrost Soils from the Lena Delta, Siberia

The methane oxidation potential of active layer profiles of permafrost soils from the Lena Delta, Siberia, was studied with regard to its respond to temperature, and abundance and distribution of type I and type II methanotrophs. Our results indicate vertical shifts within the optimal methane oxidation temperature and within the distribution of type I and type II methanotrophs. In the upper active layer, maximum methane oxidation potentials were detected at 21 °C. Deep active layer zones that are constantly exposed to temperatures below 2 °C showed a maximum potential to oxidise methane at 4 °C. Our results indicate a dominance of psychrophilic methanotrophs close to the permafrost table. Type I methanotrophs dominated throughout the active layer profiles but their number highly fluctuated with depth. In contrast, type II methanotrophs were constantly abundant through the whole active layer and displaced type I methanotrophs close to the permafrost table. No correlation between in-situ temperatures and the distribution of type I and type II methanotrophs was found. However, the distribution of type I and type II methanotrophs correlated significantly with in-situ methane concentrations. Beside vertical fluctuations, the abundance of methane oxidisers also fluctuated according to different geomorphic units. Similar methanotroph cell counts were detected in samples of a flood plain soil and a polygon rim soil, whereas cell counts in samples of a polygon centre soil were up to 100 times lower